This invention relates generally to methods for reducing the consumption of environmentally damaging fluids used in manufacturing integrated semiconductor circuits contained on wafers without any corresponding reduction in quantity or quality of production.
The present invention provides a novel method of handling corrosive fluids which provides significant environmental, engineering, and economic advantages over prior methods of fluid handling during the manufacture of semiconductor devices commonly known as integrated circuits or large scale integration (LSI).
Many different techniques have been developed in the prior art of handling fluids used in the manufacture of semiconductor wafers. Prior techniques generally handled the fluid in a tank, handled it as a spray, or handled it by evaporation. For example, the wafer etching step generally involved immersing a wafer into a bath of hydrofluoric acid etchant, or spraying the etchant, or evaporating the etchant fluid.
Each of these handling methods involves the use of excessive amounts of fluid and can impact the quickness with which the fluids effect on the wafer can be terminated, which can be critical in some manufacturing steps, such as etching. For example, one or more seconds may expire while a wafer is being removed from an immersion bath, which can cause over-etching that may ruin the wafer.
Normally more than one wafer is etched in a bath of etchant, which allows some wafers to underetch and some to overetch as oxide thickness varies from wafer to wafer. This invention allows wafers to be etched one at a time to overcome this problem.
Furthermore, the method of handling the fluid can effect contaminants in the fluid, which can destroy a wafer during a manufacturing step. For example, in order to prevent contamination of the delicate wafer surface during the immersion etching step, prior techniques generally required a total replacement of the etchant bath with each new wafer layer to be etched.
Similarly, the prior immersion and spray handling techniques were wasteful in other manufacturing steps, such as photoresist developing and stripping, by causing the use of excessive amounts of photoresist developer and photoresist stripper.
The etching and other manufacturing steps required the disposal of large quantities of very corrosive fluids, such as hydrofluoric acid (HF), sulfuric acid (H.sub.2 SO.sub.4), and other environmentally destructive fluids, which needed to be specially handled for disposal by expensive disposal means.
Furthermore, significant amounts of precious metals, such as gold, platinum, and iridium are dissolved by the etching operation at various steps in the wafer layer manufacturing process. The waste fluids are recycled to recover these precious metals. Hence, a reduction in the amount of waste fluids reduces the recycling recovery costs.
Accordingly, this invention is directed at significantly reducing the initial cost of the processing fluids and the large investment and maintenance costs needed to provide the means for recovering precious materials in the fluid waste, and for the environmental disposal corrosive waste materials resulting from the use of the fluids in integrated circuit manufacture.